Replace NULL with nullptr in all C++ files.

webrtc/tools/psnr_ssim_analyzer/psnr_ssim_analyzer.cc

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 101 matching lines @@
   parser.SetFlag("results_file", "results.txt");
   parser.SetFlag("help", "false");
 
   parser.ProcessFlags();
   if (parser.GetFlag("help") == "true") {
     parser.PrintUsageMessage();
     exit(EXIT_SUCCESS);
   }
   parser.PrintEnteredFlags();
 
-  int width = strtol((parser.GetFlag("width")).c_str(), NULL, 10);
-  int height = strtol((parser.GetFlag("height")).c_str(), NULL, 10);
+  int width = strtol((parser.GetFlag("width")).c_str(), nullptr, 10);
+  int height = strtol((parser.GetFlag("height")).c_str(), nullptr, 10);
 
   if (width <= 0 || height <= 0) {
     fprintf(stderr, "Error: width or height cannot be <= 0!\n");
     return -1;
   }
 
   CompareFiles(parser.GetFlag("reference_file").c_str(),
                parser.GetFlag("test_file").c_str(),
                parser.GetFlag("results_file").c_str(), width, height);
 }